The invention relates to improvements in friction generating devices which are used to transmit torque. Typical examples of such devices are clutch plates (also called clutch discs) which are used in friction clutches to transmit torque from a rotary driving part (such as a flywheel which receives torque from the output element of a combustion engine) to a rotary driven part (such as the input element of a variable-speed transmission in a motor vehicle). For the sake of simplicity, the improved device will hereinafter be referred to as a clutch plate with the understanding, however, that its features can be embodied in other types of friction-generating torque-transmitting devices or units.
Clutch plates to which the present invention pertains normally comprise a rotary hub (which can transmit torque to the input shaft of a transmission), a disc which is coaxial with and surrounds and is affixed to or is made of one piece with the hub, two annular friction linings one of which can be frictionally engaged by a flywheel and the other of which can be frictionally engaged by a pressure plate when the friction clutch employing the clutch plate is in actual use, and carriers which are connected to and drive the disc (and hence the hub) and are further connected to the friction linings to receive torque from the flywheel when the clutch is engaged to rotate the input shaft of the transmission in response to rotation of the flywheel. The inner diameters of the annular friction linings normally exceed the outer diameter of the disc, and the carriers normally form an annulus of pairs of confronting carriers which are affixed to the friction linings as well as to the disc and axially yieldably bear against each other.
A clutch plate of the above outlined character is disclosed, for example, in German Auslegeschrift No. 1 233 669. Each friction lining contacts two circumferentially spaced apart portions of one of each pair of carriers, i.e., a substantial portion of each friction lining remains unsupported between the two spaced apart portions of a total of one-half of the overall number of carriers. When the friction clutch employing the just described clutch plate is engaged so that the two linings are in frictional engagement with the adjacent torque transmitting and torque receiving elements of the clutch, the transmission of torque takes place only at the relatively few locations where the friction linings are in actual contact with the adjacent carriers. The non-engaged portions are free to undergo a certain amount of elastic deformation and are subject to much less pronounced wear than the actually engaged portions.
A drawback of non-uniform wear upon the friction linings is that the temperature- and/or pressure-induced deformation of friction linings is a function of the extent of wear. As a rule, the friction linings recede toward each other between the spaced-apart locations of positive contact with the adjacent carriers. This results in premature pronounced contact between large portions of the two friction linings in response to engagement of the friction clutch before the carriers have undergone full resilient deformation. As the penetration of the friction linings into the spaces between the portions of actual contact with the adjacent carriers progresses, the percentage of resilient deformability of the pairs of carriers decreases, i.e., a progressively increasing percentage of the resilient deformability of the carriers in wasted.